The invention relates to a method and a device for sorting flat mail items.
In corresponding sorting systems, the mail items are transported at high speeds and at small distances from one another, held between endless conveyor belts of a covered belt system, from a separation device to modules arranged downstream therefrom, where they are read, processed and sorted. Whilst the mail items are transported in the covered belt system, which is interrupted by points, conveyor belt disconnection points etc., the mail items can be displaced in respect of one another as a result of different physical characteristics such as for instance friction coefficients, thickness, bending strength, to a differing degree in relation to the transport means and thus as a function of the mail item sequence, thereby adjusting the gaps. The relative displacement of the mail items in respect of one another and associated therewith the partial reduction in the gaps between the mail items, which as a first approximation represents a linear function of the different transport section distances (point section and/or covered belt section) to the respective sorting terminals, mean that a set gap set in the separation device has to be travelled, above all in the case of long sorting machines with many sorting terminals, said set gap having a high percentage of probability of displacement to the machine end and the necessary minimum gap for ejection of the mail items by the points with little disruption. As only a small percentage of mail items may be discharged to reject terminals resulting from extreme displacement of the mail items in respect of each other, relatively large, standard set gaps have hitherto been set in the separation devices for each machine as a function of the machine length, to ensure reliable ejection of the mail items for all sorting terminals, thereby resulting in a reduced throughput.
In this context, U.S. Pat. No. 6,023,034 A describes a method and a device for sorting flat mail items, with which the maximum displacements occurring during transport to the sorting terminals are determined in statistical surveys as a function of the sorting terminals. A controllable gap adjustment device then allows the gaps between the mail items to be adjusted individually within the context of possible options, such that excessively small gaps are enlarged to the minimum value at the expense of subsequent larger gaps by decelerating the relevant mail item.
JP 2000-024 598 A further discloses combining the sorting terminals to form two segments arranged one behind the other and to individually adjusting the gaps as a function of the transport distance to the segments.